U.S. patent number 8,010,253 [Application Number 12/012,631] was granted by the patent office on 2011-08-30 for method for stabilizing a vehicle combination.
This patent grant is currently assigned to ZF Lenksysteme GmbH. Invention is credited to Christian Lundquist.
United States Patent |
8,010,253 |
Lundquist |
August 30, 2011 |
Method for stabilizing a vehicle combination
Abstract
A method of stabilizing a vehicle combination including a towing
vehicle and a trailer, includes determining at least one vehicle
state variable describing the state of the vehicle from a
comparison with an assigned nominal value. A correcting variable is
produced, which is supplied to an actuator in the vehicle. The
correcting variable acts upon a steering actuator in order to
adjust the wheel steering angle.
Inventors: |
Lundquist; Christian
(Linkoeping, SE) |
Assignee: |
ZF Lenksysteme GmbH
(Schwaebisch Gmuend, DE)
|
Family
ID: |
39628176 |
Appl.
No.: |
12/012,631 |
Filed: |
February 5, 2008 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20080196964 A1 |
Aug 21, 2008 |
|
Foreign Application Priority Data
|
|
|
|
|
Feb 20, 2007 [DE] |
|
|
10 2007 008 342 |
|
Current U.S.
Class: |
701/41;
180/443 |
Current CPC
Class: |
B62D
13/00 (20130101); B62D 15/025 (20130101); B62D
6/003 (20130101) |
Current International
Class: |
A01B
69/00 (20060101) |
Field of
Search: |
;701/41,42 ;180/315,443
;318/432 ;303/124,140,186 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
22 56 455 |
|
Jun 1974 |
|
DE |
|
41 27 750 |
|
Sep 1992 |
|
DE |
|
42 32 256 |
|
Apr 1993 |
|
DE |
|
198 43 826 |
|
Mar 2000 |
|
DE |
|
100 30 128 |
|
Jan 2002 |
|
DE |
|
100 34 222 |
|
Jan 2002 |
|
DE |
|
103 42 865 |
|
Apr 2005 |
|
DE |
|
Primary Examiner: Jeanglaud; Gertrude Arthur
Attorney, Agent or Firm: Jordan and Hamburg LLP
Claims
The invention claimed is:
1. A method for stabilizing a vehicle-trailer combination which
includes a towing vehicle and a trailer, the method comprising:
determining an actual value of at least one state variable
describing a corresponding state of the vehicle, the trailer or the
vehicle-trailer combination, said at least one state variable
including at least one process variable which describes a state of
the trailer or at least one other process variable from which the
state of the trailer can be derived; comparing said actual value of
said at least one state variable with a nominal value of said at
least one state variable corresponding thereto; producing a
correcting variable based on said comparing; and causing said
correcting variable to act upon a steering actuator for changing a
relevant setting thereof based on said comparing and adjusting a
wheel steering angle accordingly at least at one steerable wheel of
the vehicle-trailer combination.
2. A method according to claim 1, wherein said at least one state
variable includes a yaw rate.
3. A method according to claim 1, wherein said at least one state
variable includes a trailer angle which describes an angular
deviation between respective longitudinal axes of the towing
vehicle and of the trailer.
4. A method according to claim 1, wherein the actual value of the
at least one state variable is determined by measurement.
5. A method according to claim 4, wherein the actual value of the
at least one state variable is calculated in an observer model.
6. A method according to claim 1, wherein a compensation control is
employed using an inverse vehicle model.
7. A method according to claim 1, wherein the actual value of the
at least one state variable is determined as a function of a
vehicle longitudinal speed of the vehicle, an attitude angle and/or
friction.
8. A method according to claim 1, further comprising limiting a
difference between the actual value and the nominal value for said
at least one state variable by employing a dead time function,
wherein steering interventions are not carried out when the
difference is below a threshold value.
9. A method according to claim 1, further comprising limiting a
difference between the actual value and the nominal value for said
at least one state variable to a maximum value with by employing a
limiting function.
10. A steering system for implementing the method of claim 1,
comprising: a device for manipulating the steering; a steering
linkage; and a steering actuator.
11. A steering system according to claim 10, wherein: said system
is constructed as an EPS (electrical power steering) system; and
said steering actuator includes an electric motor.
12. The steering system according to claim 10, wherein said system
includes an AFS (active front steering) system for adjusting a
superimposing steering angle, which is superimposed on the steering
angle specified by the driver.
13. A method according to claim 1, wherein stabilization of the
vehicle-trailer combination is carried out by intervention of
steering including said causing said correcting variable to act
upon a steering actuator, and without requiring activation of a
braking system of the vehicle-trailer combination.
14. A method according to claim 1, wherein said at least one state
variable at least a respective one of a trailer angle or a trailer
yaw angle.
15. A method according to claim 1, wherein said at least one
steerable wheel of the vehicle-trailer combination includes at
least one steerable wheel of the trailer.
16. A method for stabilizing a vehicle-trailer combination which
includes a towing vehicle and a trailer, the method comprising:
determining an actual value of at least one state variable
comprising at least one process variable from which transverse
dynamics of at least one of the trailer or the vehicle-trailer
combination can be inferred; comparing said actual value of said at
least one state variable with a corresponding nominal value of said
at least one state variable; producing a correcting variable based
on said comparing; and adjusting a wheel steering angle of at least
one steerable wheel of the vehicle-trailer combination based upon
said correcting variable.
17. A method according to claim 16, wherein said adjusting includes
causing said correcting variable to act upon a steering
actuator.
18. A method according to claim 16, wherein said at least one
process variable relates to a driving state of at least one of said
vehicle, said trailer or said vehicle-trailer combination.
19. A method according to claim 16, wherein said at least one
steerable wheel is at least one steerable wheel of the vehicle.
20. A method according to claim 19, wherein stabilization of at
least one of said trailer or said trailer combination is effected
by said adjusting the wheel steering angle of the at least one
steerable wheel of the vehicle.
Description
BACKGROUND OF THE INVENTION
The invention relates to a method for stabilizing a vehicle
combination, comprising a towing vehicle and a trailer.
For stabilizing truck and trailer combinations, which include a
towing vehicle and a trailer hitched by a tow bar, DE 100 30 128 A1
discloses detecting differences between the course desired by the
driver and the actual movement of the vehicle by means of sensing
technology in the towing vehicle, and, thereupon, to braking
individual wheels of the trailer axle in order to avoid dynamic
driving instabilities by these means. As a result of braking the
trailer, the vehicle combination extends, reducing the danger of
jackknifing between the towing vehicle and the trailer.
SUMMARY OF THE INVENTION
Starting out from this state of the art, it is an object of the
invention to stabilize a vehicle combination, which comprises a
towing vehicle and a trailer, with simple means. This is to be
accomplished basically without activating the braking system of the
vehicle combination.
Pursuant to the invention, this objective is accomplished by an
approach which includes determining an actual value of at least one
vehicle state variable describing a state of the vehicle and
comparing the actual value of the at least one vehicle state
variable with a nominal value of the at least one vehicle state
variable corresponding thereto. A correcting variable is produced
based on the comparing which is supplied to a steering actuator in
the vehicle, and the correcting variable is made to act upon a
steering actuator for changing a relevant setting thereof based on
the comparing and adjusting a wheel steering angle accordingly at
least at one steerable wheel of the vehicle.
For the method of stabilizing the vehicle combination in accordance
with the invention, at least one vehicle control variable,
describing the driving state, is determined, either by measurement
or by calculation, for example, with the help of an observer, and
is used as a basis for a comparison with an assigned nominal value.
From this comparison, a vehicle control variable is produced, which
is supplied to an actuator in the vehicle for changing the current
setting. Pursuant to the invention, provisions are made so that the
control variable acts upon a steering actuator, as a result of
which the angle of the steering wheel is changed at least at one
steerable wheel of the vehicle.
In the case of a threatening instability of the vehicle composite
or of one that has already taken place, stabilization can be
carried out in this way solely by affecting the steering.
Additional stabilizing measures may be provided in the vehicle.
However, they are not necessarily required for avoiding rolling
motion of the vehicle combination. For example, it may be
appropriate to intervene in the braking process and/or in the
engine control in addition to affecting a steering. In principle,
however, intervening in the steering is sufficient for the
stabilization.
Intervention in the steering is accomplished basically over the
steerable wheels of the towing vehicle. Alternatively or
additionally, it is, however, also possible to intervene in the
steering at the trailer, provided that the latter has steerable
wheels.
In particular, the yaw rate is called upon as vehicle control
variable, which can be affected as a process variable. Additionally
or alternatively, the trailer angle, which describes the angular
deviation between the longitudinal axes of the towing vehicle and
of the trailer, can also be taken into consideration as a process
variable. In general, any vehicle state variable, from which
information concerning the transverse dynamics of the vehicle can
be inferred, comes into consideration as a process variable, that
is, any vehicle state variables or a combination hereof related to
the transverse dynamics of the vehicle. This may optionally also be
the steering angle, the transverse velocity or the transverse
acceleration or the angular velocity difference at the wheels of
the vehicle.
Linear, as well as nonlinear, control formulations can be used for
the control, which is required for stabilizing the vehicle
combination. Since the vehicle-trailer model, which forms the basis
for the control as a mathematical replacement model, is nonlinear,
a linearization about a defined operating point is required for use
as a linear controller. However, the use of nonlinear controls, for
example, of compensation controllers (also known as feedback or
feedback linearization) which is based on the fundamental principle
of an inverse vehicle model, is also possible. If the quality of
the model is adequate, the real behavior of the vehicle is
compensated for by the model and a linear control relationship
results.
It may also be appropriate to provide a limit before and/or after
the controller, in order, on the one hand, to let differences
between the nominal value and the actual value be effective only
for the case in which the difference exceeds a relevant threshold,
and, on the other, to provide a lid for the difference between the
nominal and actual values at a maximum value, in order to avoid
excessively large control interventions. For a limiter downstream
from the controller, the magnitude of the control interventions is
limited to a maximum value.
The difference between the nominal and actual values, which are to
be supplied to the controller, may optionally be subjected to
integration, in order to take the dynamics of the driving behavior
into consideration by these means. This can be accomplished by
adapting the limits in the limiter. For example, if the vehicle is
unstable over a certain period of time, the limit can be reduced,
so that the control algorithm is run through more frequently and
engages with a larger amplitude. Conversely, the limit can be
increased if the vehicle, including the trailer, runs stably for a
minimum period of time.
Advantageously, the limit is related to the difference between the
nominal value and the actual value of the vehicle control variable
under consideration. In order to establish the magnitude of the
limit of the vehicle control value in question, further vehicle
state variables and/or parameters may flow in. For example, the
attitude angle, the tire forces or the maximum friction may flow
into the limit.
The method is realized in a steering system, which has at its
disposal at least one device for manipulating the steering, usually
a steering wheel, a steering linkage and a steering actuator, the
steering angle, specified by the device for manipulating the
steering being converted with the help of the steering linkage onto
the steerable wheel of the vehicle and the steering actuator
producing a supporting moment. Alternatively or additionally to a
supporting moment, it is also possible, in the case of an
embodiment as active steering system, to specify a superimposing
steering angle, which is superimposed on the steering angle desired
by the driver. Basically, the method is suitable for use in an EPS
steering system (electrical power steering) with an electric motor
as steering actuator. However, other steering systems, such as an
electrohydraulic steering system, also come into consideration.
Further advantages and appropriate embodiments are given in the
description of the Figures and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a diagrammatic representation of a steering system in
a vehicle with a steering gear, which is preceded by a
superimposing gear;
FIG. 2 shows a diagrammatic view of a vehicle combination,
consisting of a towing vehicle and a trailer, a steering system of
FIG. 1 being realized in the towing vehicle;
FIG. 3 shows a block circuit diagram for implementing a method of
stabilizing the vehicle combination of towing vehicle and trailer;
and
FIG. 4 shows a diagram with a limiting function, which can be used
to limit the controller input and/or the controller output.
DETAILED DESCRIPTION OF THE INVENTION
A steering system 1 in a motor vehicle, shown in diagrammatic
representation in FIG. 1, comprises a device for manipulating the
steering, which is constructed as a steering wheel 2, a steering
shaft 3, which is connected with the steering wheel 2, a steering
gear 6 with a steering actuator 9 and a steering linkage 7, which
is connected with the steerable front wheels 8. The steering angle
.delta..sub.S, specified by the driver over the steering wheel 2,
is transferred over the steering shaft 3 and the steering gear 6
into a gear rack travel of the steering linkage 7, as a result of
which a wheel steering angle .delta..sub.F is set in the steerable
front wheels 8. Depending on the situation, a motor correcting
moment can be fed over the steering gear 6 into the steering system
to support the steering over the steering actuator 9, which
preferably is constructed as an electric motor. Instead of being
constructed as an electric motor, a steering actuator 9 can also be
constructed as an electrohydraulic control element.
Furthermore, the steering system 1 has a superimposing steering
gear 4 with a servo motor 5, the superimposing gear 4 being
interposed in the steering shaft 3. When the servo motor 5 is
actuated, a superimposing steering angle .delta..sub.M is produced,
which is superimposed on the steering angle .delta..sub.S, produced
by the driver, to form the resulting steering angle .delta.'.sub.S.
No superimposing steering angle .delta..sub.M is produced when the
servo motor is not in operation. In this case, the steering angle
.delta..sub.S produced by the driver is supplied directly to the
steering gear 6 as an input quantity.
It is also possible to do without the superimposing gear 4
including the servo motor 5.
The steering actuator 9 is adjusted by means of a correcting
variable S, which is produced in a regulating or controlling
device, through which the method for stabilizing a vehicle
combination passes. The correcting variable S adjusts the steering
actuator 9 and, with that, brings about the desired setting of the
front wheel angle .delta..sub.F.
FIG. 2 shows a vehicle combination 10, which consists of a towing
vehicle 11 and a trailer 12, which is coupled pivotably over a
fixed tow bar 13 to the towing vehicle 11. The front wheels 8 of
the towing vehicle 11 are constructed to be steerable. The angles
.PSI..sub.1, .PSI..sub.2 and .gamma., of which .PSI..sub.1 and
.PSI..sub.2 represent the yaw angle of the towing vehicle 11 or of
the trailer 12 and .gamma. represents the trailer angle, which
represents the angular deviation between the longitudinal axis of
the trailer 12 and the longitudinal axis of the towing vehicle 11,
are entered in FIG. 2.
FIG. 3 shows a block circuit diagram for carrying out the method.
The first block 20 represents the kinematics of the system.
Depending on the different state variables and parameters,
especially the longitudinal speed of the vehicle v.sub.x, the
maximum friction .mu..sub.max between the wheels and the road, the
attitude angle .beta. and the current wheel steering angle
.delta..sub.F, the nominal value .PSI..sub.d of the yaw rate is
determined on the basis of the kinematic relationships in block 20.
In the subsequent block 21, the dynamic vehicle behavior is modeled
by means of filters with a frequency-dependent phase shift; the
thereby obtained nominal value .PSI..sub.d of the yaw rate reflects
the dynamic vehicle behavior.
For determining the control error, the assigned actual value
.PSI..sub.m of the yaw rate is subtracted from the nominal value
.PSI..sub.d of the yaw rate in the subsequent block 22. The
difference .DELTA..PSI. between the yaw rates is supplied to a
subsequent block 23, as input value. In block 23, a limiter is
realized, which has the task of limiting the difference
.DELTA..PSI. between the yaw rates with the help of a dead-time
function in such a manner that, when the difference is below a
threshold value, steering interventions are not carried out.
Additionally or alternatively, the difference can also be capped at
a maximum. The difference function is described in FIG. 4 and will
be explained in detail there.
In addition, the longitudinal speed of the vehicle v.sub.x, the
maximum friction .mu..sub.max, the attitude angle .beta., the wheel
steering angle .delta..sub.F, as well as the difference between the
nominal value .gamma..sub.d and the actual value .gamma..sub.m of
the trailer can flow into the limiting function in block 23 as
input quantities. These state variables or parameters can be
generated in a preceding block 24, in which an observer model is
realized. The quantities sought are calculated on the basis of a
mathematical model in the observer as a function of measured state
variables or parameters, especially of the rpm of the wheels
.omega..sub.U, the steering angle .delta..sub.S specified by the
driver, as well as the actual value .gamma..sub.m of the trailer
angle.
The difference .DELTA..PSI. of the yaw rate, limited in block 23,
is supplied subsequently to block 25, which represents a
controller. A process variable, which is generally referred to as a
state variable x and is at the output of the controller, is
generated in the controller. In particular, this state variable is
a quantity, which characterizes the transverse dynamics of the
vehicle combination, such as the yaw acceleration.
In the further course, the process variable or state variable x is
supplied as input quantity to the block 26, in which a so-called
inverse mathematical vehicle model is realized. Together with the
controller in block 25, a nonlinear control formulation can be
carried out, in which the controller is constructed as a
compensation comptroller. If the inverse vehicle model in block 26
is of sufficient quality, the real vehicle, shown in FIG. 3 in
block 29, is compensated and a linear control relationship results.
State variables and parameters, generated by the observer model
from block 24 are additional input quantities in block 26. In
addition, the wheel steering angle .delta..sub.F is supplied as
input quantity in a returning loop to the inverse vehicle
model.
The inverse vehicle model supplies the superimposing steering angle
.delta..sub.M as output quantity from block 26. In a subsequent
block 27, which represents the superimposing steering gear of the
superimposing steering system and is constructed, for example, as a
planetary gear, this superimposing steering angle .delta..sub.M is
added to the steering angle .delta..sub.S, which is specified by
the driver and converted in a block 28, which represents the
steering gear. If superimposing steering is not provided in the
steering system, block 27 can also represent a moment
superimposition of an electric power steering (EPS).
The steering angle .delta..sub.1 of the driver and the
superimposition steering angle .delta..sub.M lead to a wheel
steering angle .delta..sub.F or to a corresponding correcting
variable (labeled S in FIG. 1), which is supplied as input quantity
to an actuator in the real vehicle, which is represented in block
29. Thereupon, a desired actual value .PSI. of the yaw rate sets
in. If superimposing steering is provided, the correcting variable
S is the nominal value of the superimposing steering angle
.delta..sub.M.
The yaw angle .PSI., considered in FIG. 3, is, in particular, the
yaw angle of the towing vehicle. Optionally, however, the yaw angle
of the trailer or some other state variable also comes into
consideration, especially a state variable representing the
transverse dynamics of the system.
FIG. 4 shows a limiting function, which can be used for limiting
the controller input in block 23 in FIG. 3 or the controller output
in block 26 in FIG. 3. Input and output of the limiter in FIG. 4 is
a state variable, which is generally labeled x and modulated
corresponding to the limiting function. On the one hand, the state
variable x can be subjected to a dead time, in that, below a
threshold value b, the output of the state variable is set at 0 or
at least a reduced value. The concept of "dead time" is not
time-dependent here. Instead, it is to be understood generally as a
reaction, which sets in with delay.
On the other, the state variable can be limited to a maximum value
c. The increase to the maximum value c takes place after the
expiration of the dead time at point b linearly between b and a
further ordinate value a.
The values of a, b and c may be specified as fixed values in the
limiter or calculated from vehicle state variables and/or
parameters of the vehicle.
LIST OF REFERENCE SYMBOLS
1 Steering system 2 Steering wheel 3 Steering shaft 4 Superimposing
gear 5 Servo motor 6 Steering gear 7 Steering linkage 8 Front wheel
9 Steering actuator 10 Vehicle combination 11 Towing vehicle 12
Trailer 13 Tow bar .PSI..sub.m Actual value of yaw rate .PSI..sub.d
Nominal value of yaw rate .DELTA..PSI. Yaw rate difference
.PSI..sub.1 Yaw angle of trailer .PSI..sub.2 Yaw angle of towing
vehicle .gamma. Trailer angle .gamma..sub.m Actual value of trailer
angle .gamma..sub.d Nominal value of trailer angle v.sub.x
Longitudinal speed of the vehicle .beta. Attitude angle .mu.
Friction .mu..sub.max Maximum friction .delta..sub.F Wheel steering
angle .delta..sub.S Steering angle .delta..sub.S' Resultant
steering angle .delta..sub.M Superimposition steering angle
.omega..sub.y Rpm of wheels S Control variable
* * * * *